Robot joint structure

ABSTRACT

A robot joint structure includes a first member and a second member that are hollow, an actuator that rotates the second member about a fourth axis relative to the first member, and a brake mechanism capable of braking rotation of the second member relative to the first member. The actuator includes a motor accommodated within the first member, a speed reducer that reduces the speed of rotation of a motor shaft of the motor and that transmits the rotation to the second member, a first gear provided at the motor shaft, and a second gear provided in the speed reducer and engaged with the first gear. The brake mechanism includes a brake body accommodated within the first member, a brake shaft capable of being braked by the brake body, and a third gear provided at the brake shaft and engaged with the second gear.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on Japanese Patent Application No.2019-224657, the contents of which are incorporated herein by reference.

FIELD

The present disclosure relates to robot joint structures.

BACKGROUND

A known robot joint structure includes a first arm and a second arm thatis rotatable about a rotation axis relative to the first arm. A drivingforce of a motor fixed in an accommodated state within the first arm istransmitted to the second arm via a plurality of gears and a speedreducer (e.g., see Japanese Unexamined Patent Application, PublicationNo. 2007-144559).

The motor used in the robot joint structure is normally equipped with abrake for preventing the arms from rotating in accordance with gravitywhen the power of the robot is turned off.

SUMMARY

An aspect of the present disclosure provides a robot joint structureincluding a first member and a second member that are configured tohollow, an actuator that rotates the second member about a rotation axisrelative to the first member, and a brake mechanism capable of brakingrotation of the second member relative to the first member. The actuatorincludes a motor accommodated within the first member and not having abrake, a speed reducer that reduces the speed of rotation of a motorshaft of the motor and that transmits the rotation to the second member,a first gear provided at the motor shaft, and a second gear provided inthe speed reducer and engaged with the first gear. The brake mechanismincludes a brake body accommodated within the first member, a brakeshaft capable of being braked by the brake body, and a third gearprovided at the brake shaft and engaged with the second gear.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 schematically illustrates an example of a robot equipped with ajoint structure according to an embodiment of the present disclosure.

FIG. 2 is a partially enlarged view illustrating the joint structure inFIG. 1.

FIG. 3 schematically illustrates the arrangement of components in thejoint structure in FIG. 1.

DETAILED DESCRIPTION OF EMBODIMENTS

A robot joint structure 1 according to an embodiment of the presentdisclosure will be described below with reference to the drawings.

As shown in FIG. 1, a robot 100 equipped with the joint structure 1according to this embodiment is, for example, a vertical six-axisarticulated robot. The robot 100 includes a base 110 set on a floorsurface F, and also includes a rotating body 120 supported in arotatable manner about a first axis A, which is vertical, relative tothe base 110.

The robot 100 includes a first arm 130 supported in a rotatable mannerabout a second axis B, which is horizontal, relative to the rotatingbody 120, and also includes a second arm (first member) 140 that ishollow and is supported about a third axis C, which is horizontal,relative to the first arm 130. The robot 100 further includes a hollowwrist unit (second member) 150 supported in a rotatable manner relativeto the second arm 140 about a fourth axis D, which is in a skewpositional relationship with the third axis C.

For example, as shown in FIG. 2, the joint structure 1 according to thisembodiment is disposed between the second arm 140 and the wrist unit150. The joint structure 1 includes the second arm 140, the wrist unit150, an actuator 10 that rotationally drives the wrist unit 150 aboutthe fourth axis D relative to the second arm 140, and a brake mechanism50 that brakes the wrist unit 150 relative to the second arm 140.

The actuator 10 includes a speed reducer 30 and a motor 40. The speedreducer 30 includes an input shaft 31 fixed to the second arm 140, andalso includes an output shaft 34 that is supported in a rotatable mannerabout the fourth axis D relative to the input shaft 31 and that is fixedto the wrist unit 150.

The speed reducer 30 includes a hollow section 33 extending along thefourth axis D at a position including the fourth axis D. The speedreducer 30 includes a second gear 32 located at the second arm 140 sideof the input shaft 31 and supported in a rotatable manner about thefourth axis D relative to the input shaft 31.

The second gear 32 has a ring shape with a center hole 35 that spatiallycommunicates with the hollow section 33. Thus, the internal space of thesecond arm 140 spatially communicates with the internal space of thewrist unit 150 through the hollow section 33 and the center hole 35.

The motor 40 is fixed to the second arm 140 in a state where the motor40 is accommodated within the second arm 140. The motor 40 includes amotor shaft 41 that extends in the axial direction. A first gear 42 isfixed to the motor shaft 41.

As shown in FIG. 3, the motor 40 is fixed to the second arm 140 at aposition offset radially outward from the fourth axis D to avoid overlapwith the hollow section 33 and the center hole 35. The first gear 42fixed to the motor shaft 41 is engaged with the second gear 32 of thespeed reducer 30.

Accordingly, rotation of the motor shaft 41 of the motor 40 istransmitted to the speed reducer 30 via the engagement between the firstgear 42 and the second gear 32, is reduced in speed within the speedreducer 30, and is output as rotation of the output shaft 34 of thespeed reducer 30.

The brake mechanism 50 is accommodated within the second arm 140 andincludes a brake body 53 fixed to the second arm 140 and a brake shaft51 supported in a rotatable manner relative to the brake body 53. Athird gear 52 engaged with the second gear 32 is fixed to the brakeshaft 51.

As shown in FIG. 3, the brake mechanism 50 is also fixed to the secondarm 140 at a position offset radially outward from the fourth axis D toavoid overlap with the hollow section 33 and the center hole 35. Themotor 40 and the brake mechanism 50 are disposed at different positionsset apart from each other in the circumferential direction around thefourth axis D.

The operation of the joint structure 1 according to this embodimenthaving the above-described configuration will be described below.

In the joint structure 1 according to this embodiment, when the motorshaft 41 of the motor 40 is rotated, the rotation of the motor shaft 41is transmitted to the speed reducer 30 via the engagement between thefirst gear 42 and the second gear 32, so that the wrist unit 150 isrotated about the fourth axis D relative to the second arm 140.

Because the third gear 52 is also engaged with the second gear 32 at thesame time, the brake shaft 51 is rotated via the third gear 52 when thesecond gear 32 rotates. Therefore, when the brake body 53 is actuated,the brake shaft 51 is stopped from rotating, and a braking force istransmitted to the speed reducer 30 via the engagement between thesecond gear 32 and the third gear 52. Accordingly, the wrist unit 150can be maintained in a stationary state relative to the second arm 140.

In this case, in the joint structure 1 according to this embodiment, themotor 40 and the brake mechanism 50 are separated from each other andare disposed at different positions in the circumferential directionaround the fourth axis D, so that the height of the motor 40 in theaxial direction can be reduced and distributed, as compared with abrake-equipped motor. This is advantageous in that the internal space ofthe second arm 140 can be minimized, and that the outer dimensions ofthe second arm 140 can be reduced.

In the joint structure 1 according to this embodiment, the motor 40 andthe brake mechanism 50 are disposed at offset positions where they donot overlap with the hollow section 33 of the speed reducer 30 and thecenter hole 35 in the second gear 32. Accordingly, a wiring member (notshown) can be routed from the second arm 140 to the wrist unit 150through the hollow section 33 and the center hole 35.

As shown in FIG. 2 and FIG. 3, the joint structure 1 according to thisembodiment is provided with a first section 141 extending along thefourth axis D and a second section 142 bending in one direction relativeto the first section 141 and extending in a direction intersecting thefourth axis D. Accordingly, the second arm 140 has a shape of the letterL obtained by connecting the first section 141, which is cylindrical,and the second section 142, which is cylindrical, with a bent section.

With regard to the internal space of the second arm 140 having thisstructure, the space within the first section 141 widens in onedirection at the bent section. In this embodiment, this widened shapewithin the bent section is utilized to dispose the motor 40 in aposition across both sides of a surface extended from the outer surfaceof the first section 141 along the fourth axis D.

Accordingly, even with the motor 40 being offset significantly to aposition where it does not overlap with the hollow section 33 and thecenter hole 35, the outer dimensions of the second arm 140 do not needto be increased. This is advantageous in that further compactness can beachieved.

Specifically, by effectively utilizing the internal space in the bentsection of the second arm 140, the outer diameter of the first section141 of the second arm 140 around the fourth axis D can be reduced.

Furthermore, the outer diameter of the wrist unit 150, supported in arotatable manner about the fourth axis D relative to the second arm 140,around the fourth axis D can also be reduced. This is advantageous inthat the entire robot 100 can be reduced in size and weight.

This embodiment is based on the assumption that the motor 40 and thebrake mechanism 50 are separated from each other to prevent an increasein size of the second arm 140. Alternatively, the advantage of reducingthe outer dimensions of the first section 141 of the second arm 140 bydisposing the motor by utilizing the shape of the internal space in thebent section of the second arm 140 can also be achieved by employing abrake-equipped motor as the motor.

The invention claimed is:
 1. A robot joint structure comprising: a firstmember and a second member that are hollow; an actuator that rotates thesecond member about a rotation axis relative to the first member; and abrake mechanism capable of braking rotation of the second memberrelative to the first member, wherein the actuator includes a motoraccommodated within the first member and not having a brake, a speedreducer that reduces the speed of rotation of a motor shaft of the motorand that transmits the rotation to the second member, a first gearprovided at the motor shaft, and a second gear provided in the speedreducer and engaged with the first gear, and the brake mechanismincludes a brake body accommodated within the first member, a brakeshaft capable of being braked by the brake body, and a third gearprovided at the brake shaft and engaged with the second gear, whereinthe first member includes a first section extending along the rotationaxis, a second section extending in a direction intersecting therotation axis, and a bent section provided between the first section andthe second section, and, in a bent space of the bent section, the motoris disposed along the rotation axis.
 2. The robot joint structureaccording to claim 1, wherein the speed reducer includes a hollowsection including the rotation axis and extends through the speedreducer along the rotation axis, the second gear is supported in arotatable manner about the rotation axis and has a ring shape with acenter hole, and the first gear and the third gear are supported in arotatable manner about axes that are parallel to the rotation axis andthat are set apart from each other in a circumferential direction.